This invention pertains to medical implantable devices and particularly to spinal implants. Various devices for internal fixation of bone segments in the human or animal body are known in the art. The most common types of spinal implant systems are hook and rod systems and pedicle screw systems which provides a means of gripping a spinal segment. These implant systems are often used in conjunction with another implant device to be positioned in an intervertebral disc space between the ends plates of adjacent vertebral bodies for fixing the relative locations of the end plates. However, both hook and rod and pedicle screw systems have limitations and are not appropriate for all types of spinal disorders.
Conventional hook and rod systems comprise a series of hooks and an elongate rod. Typically, the hooks are positioned against lamina which are not adjacent one another to decompress or compress a section of the spine. Further, the hooks are positioned before being connected to the connecting rod, requiring the surgeon to place each individual hook before attempting to mount the connecting rod onto the hooks.
A conventional pedicle screw system comprises a pedicle screw and a rod-receiving device. The pedicle screw includes an externally threaded stem and a head portion. The rod-receiving device couples to the head portion of the pedicle screw and receives a rod (commonly referred to as a distraction rod). Two such systems are inserted into respective vertebrae and adjusted to distract and/or stabilize a spinal column. The pedicle screw does not, by itself, fixate the spinal segment, but instead operates as an anchor point to receive the rod-receiving device, which in turn receives the rod. One goal of such a system is to substantially reduce and/or prevent relative motion between the spinal segments that are being fused.
The implantation of pedicle screw systems are intricate, time consuming, and invasive into the spine of the patient. Typically, a series of pedicle screws must be carefully placed precisely in the narrow pedicle region of the spine. These pedicle screws are then fitted with rod receiving devices which are then in turn fitted with distraction rods. The system of screws and rods creates an intricate system for supporting the spine that takes considerable effort.
The placement of the hooks, screws and rods is time consuming because the components must be positioned through trial and error with repeated adjustment of position of the components until final proper positioning of all the components of the entire system is achieved simultaneously. In addition, the implantation of pedicle screw systems is highly invasive because screws must be deeply driven into the pedicle region of the spine within close proximity of the nerves of the spinal cord or spinal nerves branching off of the spinal cord. Further, the rod is positioned out from within the intervertebral space, resulting in a larger overall implant assembly being implanted in the spinal area.
Other implant devices which are generally less time consuming to install and which are contained within the intervertebral space between adjacent vertebral bodies are known. Generally, these implant devices include a reduced profile orientation to assist in implantation of the implant device. The implant devices further include a predetermined enlarged profile orientation, such that as the implant device is shifted from the reduced profile orientation to the enlarged profile orientation the implant device engages the opposing laminar surfaces and separates the laminar surfaces to provide a desired, predetermined distraction distance. However, unlike the pedicle screw and rod systems, these implant devices are not configured to variably distract the engaged laminar surfaces to adjust for the geometries of an individual spine. As such, multiple implant devices may need be inserted and removed to ensure that the geometries of spine and the desired distraction distance are provided for.